The present invention relates to an image forming apparatus in which a toner replenishment device, which can automatically replenish toner supplied from a toner replenishment container (hereinafter called toner cartridge) to a developing unit, is provided.
In a color image forming apparatus, a plurality of developing units, in which four color toners of yellow, magenta, cyan and black, are respectively accommodated, are used. Accordingly, exclusive use toner replenishment devices are respectively provided to respective developing units. When the amount of toner remaining in the toner replenishment device is decreased, or image density is reduced, this condition is detected by a detecting means. Predetermined color toner is supplied from the corresponding toner cartridge to the toner replenishment device in which the amount of toner has been decreased.
This toner supply to the toner replenishment device is carried out as follows. The amount of toner remaining in the toner replenishment device is detected. According to the detection signal, the toner cartridge, in which corresponding color toner is accommodated, is attached to the toner replenishment device. Toner is fed into the toner replenishment device for replenishment. At this time, the toner cartridge is structured such that it can be attached to only the corresponding toner replenishment device, preventing erroneous attachment to other color toner replenishment devices.
In the present invention, as described above, a structure in which only the corresponding toner cartridge is attached to the toner replenishment device, in which toner replenishment is needed, is provided to the toner replenishment device in which four color toners are respectively accommodated. As the above-described safety means, a means is provided in which a toner cartridge, on a portion of which the same color of cyan, for example, is provided, is made for a cyan toner replenishment device so that a different color toner can not be supplied. Further, as described above, a mechanism is provided, by which only the cyan color toner cartridge, for example, can be attached to the cyan toner replenishment device. Although the above-described safety means is provided, the cyan toner cartridge, for example, can be attached to the cyan toner replenishment device even when toner is not insufficient in the toner replenishment device. Accordingly, in the case where another new toner cartridge is attached to the toner replenishment device and toner is replenished, toner is unusually excessively replenished. Then, when the toner cartridge is detached from the toner replenishment device, toner overflows from a toner supply opening, and the toner drops into the image forming apparatus. Further, a passage between the developing unit and the toner replenishment device is clogged with toner when toner is so excessively supplied, so that toner can not be properly replenished to the developing device.